i would like to replace the Heatrae Stradia shower that i have with a new Mira shower as the old one is pretty pathetic.

i was looking to install an 8.5kw shower, the old shower runs on a 30 amp fuse, can i install a 8.5kw using the same 30amp or will i have to replace the amp. looking at the maths 8500/230 = 39.9amp can a 30amp cope with that? Not sure what KW the old shower runs at can find it.

Looks Llke you may need higher protective device(fuse) this could also mean your cable size is not a safe size to carry new higher current and if so needs to be updated.
So then new circuit will require RCD/RCBO protection and becomes notifiabe work. Under part p of building regulations which is law.(projects page part p)
So I suggest you call a registered domestic installer who can self cert his own work. It will save you money in the long run as a fee of 130GPB would be charge by Building Controls and you would still need to install it and buy materials.
KB

hi, you have answered your own question, no a 30A fuse/mcb won't run at 40A for more than a very short time, it needs a 40A rating but it can't just be changed as wiring may not be safe at 40A, isolator switch may be only 30A rated cable size, route/length all need to be assessed by qualified leckie,
regards SPARX

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